The trailer is one of the most important aspects in film marketing.
Make sure the 'trailer' app is activated. You can do this under Settings -> Apps & Integrations
Then, visit Content -> Trailer in the left hand navigation bar of your Assemble dashboard.
This will bring you to your trailer page.
Click the 'trailer settings' tab at the top of your trailer editing dashboard in the Trailer App.
Paste the http address of your trailer on Vimeo or Youtube.
Anytime you update your trailer file on Vimeo or Youtube, it will automatically update on Assemble.
Updated: April 2020